Description

Adds a line segment to the path from the current point to the beginning of the current sub-path,
(the most recent point passed to CairoContext::moveTo()),
and closes this sub-path. After this call the current point will be at the joined endpoint
of the sub-path.

The behavior of close_path() is distinct from simply calling
CairoContext::lineTo() with the equivalent coordinate in the case of
stroking. When a closed sub-path is stroked, there are no caps on the ends of the sub-path.
Instead, there is a line join connecting the final and initial segments of the sub-path.

If there is no current point before the call to CairoContext::closePath(),
this function will have no effect.